Viscosity

noun (uncountable/countable)

/vɪˈskɒsɪti/

Viscosity is a measure of a fluid's internal resistance to flow or deformation, arising from intermolecular friction; it is quantified as the ratio of shear stress to shear rate, with the SI unit pascal-second (Pa·s) or poise (P). Highly viscous fluids (honey, molasses, bitumen) flow slowly; low-viscosity fluids (water, air) flow easily. In petroleum engineering, the viscosity of crude oil critically determines pipeline design and refining processes; India's state-owned Indian Oil Corporation manages viscosity-graded fuel products across its refinery network, and the viscosity of blood plasma is a clinical diagnostic parameter for conditions like polycythaemia.

✍️ Usage in a UPSC answer

The seasonal viscosity variation of bunker fuel used by Indian Ocean commercial shipping increases the risk of engine fouling in low-temperature conditions, driving the International Maritime Organization's mandate for low-sulphur, optimised-viscosity fuels under MARPOL Annex VI.

Synonyms

internal frictionresistance to flowfluidity (inverse)thickness (colloquial)stickiness

Antonyms

fluidityinvisciditysuperfluidity (at quantum scale)

🌱 Word Family

viscous (adjective), viscously (adverb), viscometer (noun), inviscid (adjective — having zero viscosity), viscoelastic (adjective)

🔡 Root

Medieval Latin viscosus = sticky; from viscum = mistletoe, birdlime (a sticky substance made from mistletoe berries)

📜 Etymology

The word derives from Medieval Latin viscositas (stickiness), from viscosus (sticky, glutinous), itself from Latin viscum (mistletoe or the sticky birdlime made from its berries, used to trap birds). The Romans smeared viscum-derived paste on branches to catch birds, making viscum synonymous with stickiness. The modern physical concept of dynamic viscosity was formalised by Isaac Newton in his Principia Mathematica (1687), though the Latin terminology entered scientific English gradually through the 18th–19th centuries.

🧠 Memory Hook

Viscosity comes from viscum (birdlime — the sticky paste from mistletoe). Romans used this ultra-sticky substance to trap birds; the stickier it was, the harder to flow. A viscous fluid is like birdlime — it resists flowing, just as birdlime resisted birds escaping.

⚗️ General Science 📖 Seen in: Human Body Systems — Organ Systems, Ph...

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